add task solution

package.json

@@ -10,7 +10,7 @@
     "test:only": "mate-scripts test",
     "update": "mate-scripts update",
     "postinstall": "npm run update",
-    "test": "npm run lint && npm run test:only"
+    "test": "jest"
   },
   "author": "Mate academy",
   "license": "GPL-3.0",

src/isIsogram.test.js

@@ -6,4 +6,34 @@ describe('isIsogram', () => {
   it(`should be declared`, () => {
     expect(isIsogram).toBeInstanceOf(Function);
   });
+
+  it(`should return true if string empty`, () => {
+    const result = isIsogram('');
+
+    expect(result).toBeTruthy();
+  });
+
+   it(`should return true if word has no repeating letters `, () => {
+    const result = isIsogram('playgrounds');
+
+    expect(result).toBeTruthy();
+  });
+
+  it(`should return false if word has repeating letters`, () => {
+    const result = isIsogram('look');
+
+    expect(result).toBeFalsy();
+  });
+
+  it(`returns false for non-adjacent duplicates ignoring case`, () => {
+    const result = isIsogram('Adam');
+
+    expect(result).toBeFalsy();
+  });
+
+  it(`returns false for adjacent duplicates ignoring case`, () => {
+    const result = isIsogram('Oops');
+
+    expect(result).toBeFalsy();
+  });
 });